According to prior art submicron amorphous silicon dioxide particles are produced from the off-gases from furnaces such as silicon- and ferrosilicon furnaces. Elkem AS has for many years been developing the technology concerning the off gases from different furnaces and the production of fine amorphous silicon dioxide particles (microsilica). The microsilica particles generally have a particle size of about 0.15 microns and a surface area (BET) of between 20 and 30 m2/g. The relatively high specific surface area is for some applications, such as concrete, a disadvantage due to low flow properties of the microsilica particles.
The amorphous silicon dioxide particles obtained from the above process do however have the drawback that the composition and colour vary with varying furnace operation and also with varying raw materials used for the production of silicon or ferrosilicon. The SiO2 content may thus vary from 99% by weight down to 70% by weight and the colour may vary from black to white.
Fine amorphous silicon dioxide particles are used in numerous applications such as concrete, refractory materials, ceramic materials, filler in plastic and rubber.
It is further known to produce submicron silicon dioxide particles by burning inorganic silanes. This process is however very costly.
The object of the present invention is thus to provide a stable and accelerated process for producing spherical submicron amorphous silicon dioxide particles having a high and consistent purity and a consistent colour.